The present invention relates to solid lubrication tools and, in particular, to tools in which packed solid lubrication material forms a major structural component and methods for producing and using such tools.
The lubrication of parts which are in moving contact with each other is necessary in order to maintain and protect the integrity of the respective parts and thereby permit continued efficient functioning of the apparatus in which the moving parts resides.
Solid lubricant materials are known as an alternative to oils and greases for lubrication, particularly in high temperature applications where oils and greases are not effective. Solid lubricants are thin films composed of a single solid or a combination of solids introduced between two rubbing surfaces for the purpose of reducing friction and wear.
Graphite and molybdenum disulfide are the most frequently used inorganic solid lubricants. Other examples of solid lubricant materials include, but are not limited to, lithium fluoride, graphite fluoride, lead oxide, lead sulfide, lead, tin, gold, copper, zinc, silver, barium fluoride, calcium fluoride, and combinations of these materials with or without other admixtures. For high temperatures, some solid lubricants have very important advantages, including high chemical stability, high melting point, low volatility, the absence of viscosity effects, and a general absence of any chemical reaction with other materials.
In order for a solid lubricant composition to be effective it should adhere, or be made to adhere, to one or both of the bearing surfaces so that it is not rapidly lost from the mating surfaces. Further, it should provide low but consistent friction between two surfaces and it should have a sufficient wear resistance. Solid lubricants can be used in many different forms, including (a) as free powder (b) as suspension (c) burnished onto a surface by rubbing (d) applied as a coating mixture, etc.
Among the disadvantages of solid lubricants, when compared to oils and greases, is the difficulty of applying the solid lubricant onto a substrate and replenishing it when it reaches the end of its useful life. One approach to this problem employs embedding significant quantities of lubricant material within cavities or grooves within machine components. Examples of this approach may be found in U.S. Pat. Nos. 5,322,372 to You and 5,516,213 to Moriyama et al. However these implementations require redesigning of the components in question to accommodate the lubricant material. U.S. Pat. No. 5,388,631 to Sagantuma et al. discloses application of solid lubricant in situ in the form of a suspension of particles in water supplied as a spray. This also requires adaptation of the machine structure.
An alternative approach is disclosed by U.S. Pat. No. 4,900,579 to Lee et al. which teaches a burnishing process through which solid lubricant powder is bonded to a surface by rubbing under applied pressure and heat. Lee et al. propose the use of a very fine powder particle size so as to fill depressions and pores in the treated surface, thereby leveling the surface on a microscopic scale. This provides a longer lasting lubricating effect. The treatment process described would, however, be prohibitively labor intensive and expensive to implement in standard production procedures.
Finally, in the field of railway engineering, U.S. Pat. No. 5,251,724 to Szathowski et al. exemplifies a system for reducing friction between train wheels and a track by continuous rubbing contact of a solid lubricant material. U.S. Pat. No. 4,915,856 to Jamison discloses a corresponding solid lubricant composition. Jamison proposes a lubricant based on a polymeric carrier with additives including solid lubricants, oils and surface agents. While such a composition may be suited to railway applications, they are not generally appropriate for use with internal components of machines where carrier residues may be deposited.
There is therefore a need for tools for applying solid lubricant which would achieve a long lasting lubricating effect through simple rubbing application, and methods for producing such tools. It would also be highly advantageous to provide methods for using such tools which wold be fully compatible with conventional machining tools and techniques.